@ razpag
The way I understand matters is as follows (please correct me wherever I have got it wrong):-
Via ADSL, the DSLAM is located at the exchange.
Via FTTC, the DSLAM is located at the FTTC cabinet, effectively bringing the exchange a lot closer to the end users (for broadband purposes).
The broadband speed at the FTTC cabinet is currently restricted to 40 Mb (for now), & will always be a minimum of 40 Mb
The telephone service still comes via wires (copper or ally, or a mixture) all the way from the exchange to the old cabinet
The broadband fibre & telephone wires only join up at the FTTC cabinet
The broadband & telephone services are then delivered to end users from the FTTC cabinet via wires
The wires between the cabinet & the end user can often take quite a detour, increasing the line length that actually affects broadband speeds substantially in some cases
The overall length of the wires from the cabinet to the end user has a distinct effect upon Line Attenuation
Line attenuation can additionally increase due to the conductive material the wire is made from e.g. copper conducts much better than aluminium, the thickness (poundage) of the wire, the quality of any joints, corrosion, water ingress, temperature.
Line Attenuation directly affects the broadband speed at the end user's master socket i.e. the longer the line, the higher the attenuation & the lower the broadband speed at the master socket
End users very close to the FTTC cabinet (within 100m or so) can expect the full 40 Mb, less any general overheads. The usual full speed is around 39 Mb at the master socket.
Broadband speeds graually decrease over a line length of around 700m - 800 m, then rapidly decrease thereon after as the Line Attenuation increases due to the general resistance within the wires.
At a distance from the cabinet of say 750 m, assuming the wires are in good condition, a reasonable line speed of 35 Mb can be expected. Allowing for general overheads, an achievable & sustainable download speed of 33 Mb can be expected, suject to contention.
Signal to Noise Ratio also affects line speed. A high SNR = good, a low SNR = bad.
Electrical noise can be introduced into the line from various sources e.g. induction from street lights, nearby power cables, radio frequency transmissions, fridge motors etc.
SNR is usually at its best during the daytime. In the evenings, SNR can lower substantially
Line speeds & therefore upload/download speeds are continually & automatically adjusted by Dynamic Line Management (DLM) to suit prevailing line conditions.
Following initial installation, the DLM will allow the highest speed possible to the master socket, constantly checking for things such an increase in attenuation, a lowering of SNR (the more interference, the lower the SNR), regular disconnections for whatever cause.
To keep the line working, the DLM will lower the line speed to restrict errors & maintain stability.
Over the first 10 days or so, the line speed usually trains & stabilises at a sustainable value, although a succession of incidents such as repeated disconnections can restart the line training period at any given time.
Line speeds are lowered quite quickly by the DLM, & via FTTC can take around 10 days or so to recover to the previous sustainable speeds.
Now, in my own circumstances, for the first couple of weeks, I solidly achieved download speeds of 32-33 Mb, against the installing engineer's confirmation of a line speed (Maximum Rate) of 35(ish) Mb.
Following a number of disconnections & a complete loss of phone & broadband service for 4 days, the line speeds eventually reduced to around 8.5 Mb.
Every now & then the line would pick up speed, but would be reduced a short time later by another succession of disconnections.
Having sustained download speeds of around 32-33 Mb for a couple of weeks, my line can be considered to have completed its training period, & given another suitable training period with very few disconnections, high resistance, other interference etc. may be expected to gradually regain those sort of speeds.
this may take another 10 days or so.
It is my understanding that DLM adjusts line speeds "on the fly" & does not in itself cause disconnections.
I assume therefore that the disconnections have been intermittently caused by other unknown events.
There does not appear to be a pattern to these events.
The weather can be warm & dry, or wet, cold & windy.
It could be during the daytime or at evenings, or even the early hours of the morning.
A number of days can pass with no disconnections, sometimes spanning whole weekends.
My line currently does appear to have quite a high attenuation in comparison to its likely overall physical length. This suggests high resistance, but of an intermittent nature, otherwise, surely I could never have achieved the initial high download speeds.
It is however impossible to monitor line/connection statistics via the BT modem.
The cynics amongst us may well believe this was an intentional move by BT, purely with the aim of concealing the facts that FTTC isn't quite ready for the market as advertised & is only really fit for purpose for anyone living within 100m or so of the FTTC cabinets.
Maybe the new & improved version 2B modem will be nore resilient to these intermittent events.
As the "special" engineer didn't test the quality of the line in any way, the question regarding general line quality cannot be answered at this stage.
In your opinion, is this matter really worth pursuing? I won't give up if there is a reasonable chance of a permanent reolution, but I don't wish to keep flogging a dead horse.
In many respects I should be happy with my current download speeds of around 22 Mb (it is after all a lot more than many users can achieve), but in reality it is only just over half the speed that FTTC promises.
Sorry for the length & rambling nature of this post. Do you have any experienced comments or advice for me?
Paul
Edit: Have BT or Plusnet manually introduced a Max Rate cap onto my line, that could/should now be removed to at least test the line at full speed again?
The engineer said he didn't test the speed as it leaves the DLM at the FTTC cabinet as that wasn't his job.
Would this be a basic test that "special" engineers should do as part of an investigation into poor speeds at the end users master socket? I know it would be if I was investigating for example poor water pressure at a tap. I would first check that the pressure at the source (mains) was O.K., especially if it was a known fact that it had been good pressure at the tap at one time.